Suppressing the liquid product crossover in electrochemical CO₂ reduction

Coupling electrochemical CO₂ reduction (CO₂R) with a renewable energy source to create high-value fuels and chemicals is a promising strategy in moving toward a sustainable global energy economy. CO₂R liquid products, such as formate, acetate, ethanol, and propanol, offer high volumetric energy density and are more easily stored and transported than their gaseous counterparts. However, a significant amount (~30%) of liquid products from electrochemical CO₂R in a flow cell reactor cross the ion exchange membrane, leading to the substantial loss of system-level Faradaic efficiency. This severe crossover of the liquid product has—until now—received limited attention. Here, we review promising methods to suppress liquid product crossover, including the use of bipolar membranes, solid-state electrolytes, and cation-exchange membranes-based acidic CO₂R systems. We then outline the remaining challenges and future prospects for the production of concentrated liquid products from CO₂.